Earth Science

Minerals

Merrill Chapter 4 Notes

4-1 The Rock Cycle

Rock-is a mixture of minerals, mineraloids, glass, or organic matter.

Common rock forming minerals are quartz and feldspar.

Rock Cycle:

Check figure 4-2 in the text!

Summary:

Rocks are changed by many different processes: weathering, erosion, compaction, cementation, melting, and cooling.

Draw your own Rock Cycle to use for your test!

4-2 Igneous Rocks

Igneous rocks are formed when molten material (magma or lava) cools and hardens.

Lava is magma that has reached the surface of the earth.

Intrusive Igneous rocks are rocks formed by magma cooling below the earth’s surface. They form very large crystals (*****) because they cool very slowly.

Extrusive Igneous rocks are rocks formed by Lava cooling on the earth’s surface.

They form small crystals (*****) because they cool rapidly.

Classification of Igneous rocks: Based on Mineral Type

Basaltic: are dense, heavy, dark-colored rocks. Rich in iron and magnesium.

Granitic: are light-colored rocks, and are less dense then basaltic rocks. More silicon and oxygen.

Andesitic rocks have a mineral composition between the basaltic and granitic rocks.

Igneous Rocks are the most abundant type of rocks.

4-3 Metamorphic Rocks

Metamorphic Rocks- are rocks that have changed due to temperature and pressure increases or they undergo changes in composition.

-They are formed from igneous, sedimentary, or from other metamorphic rocks.

Classification of Metamorphic Rocks: Based on the presence of mineral grains in a banded appearance.

Foliated Metamorphic Rocks: have mineral grains in parallel bands. Examples are gneiss and slate

Nonfoliated Metamorphic Rocks: have no banding. Example is quartzite (metamorphosized sandstone)

4-4 Sedimentary Rocks

Sedimentary Rocks form when sediments become pressed or cemented together or when sediments precipitate out of solution.

Sediments: are loose materials such as rock fragments, mineral grains, and bits of organic material.

Erosion transports and deposits sediments – upper layers put pressure on lower= compaction.

Cementation- when particles or sediment are “glued together” by natural cements.

Classification of Sedimentary Rocks: Based on their composition and formation process.

Clastic Sedimentary Rocks: made of broken fragments of rock or organic materials.

Ex. Conglomerate, sandstone, and shale.

Chemical Sedimentary Rocks: formed minerals that have precipitated out of solution. Ex. Calcite

Organic Sedimentary Rocks: formed from once living things. Ex. Coal and some limestone

Rocks are continually changing from one form or type to another: The Rock Cycle!